PROJECTSUMMARY Theobjectiveofmylaboratoryistocharacterizehowmolecularcommunicationbetweenbacteriaandtheir animalhostsleadstospecificandreproduciblecolonization.Toaccomplishthisgoal,thelaboratorystudiesthe V.fischeri-squidsystem.Thissystemisadvantageousbecausebacteriacolonizethroughthenaturalrouteof infection,allanimalsarecolonizedwithinthreehoursofbacterialinoculationintotheseawater,thebacteria canbesubjecttodetailedgeneticmanipulation,andtheprecisesiteofinfectioncanbeimageddirectlyinthe liveanimalhost,allowingforcuttingedgegeneticandgenomicapproaches.Focusingonhowsquidare reproduciblycolonizedbythespecificsymbiont,totheexclusionofthemillionsofcompetingbacteriain seawater,hasrevealedkeyrolesforbacterialaggregationandbiofilmformationinpromotingspecifichost- microbeinteractions.Recentlyourglobalgeneticscreentoidentifycolonizationfactorsrevealedmultiplenovel biofilmactivatorsandidentifiedanorphanhistidinekinase,whichactsasanegativeregulatorofSypbiofilm developmentinvivo.Toelucidatethepathwaysgoverningcolonizationandbiofilmdevelopmentintheanimal hostwewill(1)dissectthemoleculardetailsofthenovelhistidinekinasepathway,(2)defineathightemporal andspatialresolutionthestepsnecessaryfortheestablishmentofthismutualisticrelationship,and(3) characterizetheroleofnewcolonizationfactorsusinggeneticandmetabolomicapproaches.Sincethe strategiesusedbyV.fischeritointeractwithitshostareconservedinotherhost-microbesystems,ourfindings willbeapplicabletounderstandotherbeneficialassociationsaswellasinteractionsbetweenpathogenic bacteriaandtheirhosts.